1. Action Potential Lesson 11
Neural Communication
Action Potential
Lesson 11

2. Action Potentials Large and rapid change in membrane potential
electrically-gated channels
EPSPs
threshold potential
Occurs in axon
triggered at axon hillock ~

3. axon hillock

4. AP Characteristics Voltage-gated channels All or none Slow
Non-decremental
Self Propagated
regenerated ~

5. -65
-55
+40
-75
Time Vm

6. -65
-55
+40
-75
Time Vm

7. -65
-55
+40
-75
Time Vm

8. -65
-55
+40 75
Time Vm

9. Vm drive Na+ into cell +40 -55 -65 -75 Time C & E gradients
Depolarization
Na+ influx Vm
-55
-65
-75
Time

10. Vm Amplitude = 105 mV +40 - 65 mV to +40 mV -55 -65 -75 Time
Depolarization
Na+ influx
- 65 mV to +40 mV Vm
-55
-65
-75
Time

11. +40
Repolarization
K+ efflux Vm
-55
-65
-75
Time

12. +40
After-
hyperpolarization Vm
-55
-65
-75
Time

13. Refractory Period after AP won’t fire again relative & absolute
during after hyperpolarization
requires greater depolarization ~

14. Relative Refractory Period
+40
Time Vm
-55
-65
-75

15. Absolute refractory period
Na+ channels deactivate
will not trigger AP
must reset
Ball & Chain Model ~

16. Na+ channel deactivation

17. Na+ channel deactivation

18. Frequency Code Pattern = Intensity of stimulus frequency of APs
Place = type of stimulus
Visual, auditory, pain, etc.
Brain area that receives signal
Doctrine of Specific Nerve Energies ~

19. FREQUENCY CODE Weak stimulus 1. Moderate stimulus 2. Strong stimulus3.

20. Saltatory Conduction Myelinated neurons
oligodendroglia & Schwann cells
Transmit long distances
APs relatively slow, regenerates
EPSPs - fast, decremental
Saltatory: combines both types of current
speed without loss of signal ~

21. Saltatory Conduction Nodes of Ranvier action potentials Myelinated
like electricity through wire
decremental but triggers AP at next node
Safety factor - trigger AP across 5 nodes
mm apart
larger neurons  farther apart ~

22. Saltatory Conduction
Nodes of Ranvier

23. PSPs vs APs Graded longer duration chemical-gated passive spread
Summation
longer duration
* msec
chemical-gated
passive spread
instantaneous
decremental
All-or-none
short
1-2 msec
voltage-gated
propagated
slow
nondecremental